The no-dash and -1 Models 586, 686, 581 and 681 had a problem with the firing pin and bushing design that allowed primer cup material in the case of certain high-pressure loads to flow back into the gap between the two, potentially binding the cylinder. S&W redesigned the parts (the redesign being incorporated into the -2 variations) and issued a recall for the earlier guns. Guns that have been sent back to have the new parts installed are stamped with an "M" in the frame cutout near the model number. S&W will still make this modification at no cost and will cover shipping both ways. The appearance of the gun is not changed in any way.